Collector configured of mirror shells

ABSTRACT

There is provided a collector. The collector includes a first mirror shell positioned inside a second mirror shell that has a chamfered end.

BACKGROUND OF THE INVENTION

The present invention relates to a collector for illumination systemsusing a wavelength ≦193 nm, preferably ≦126 nm, particularly preferablywavelengths in the EUV range, for absorbing light emitted by a lightsource and for illuminating a region in a plane using a plurality ofrotationally symmetric mirror shells which are positioned one insideanother around a common axis of rotation. One ring aperture element ofthe object-side aperture is assigned to each mirror shell. Therotationally symmetric mirror shells include at least one first mirrorsegment having at least one first optical surface. A starting point andan end point are assigned to the first optical surface in relation tothe axis of rotation, the starting point defining an outer edge beam andthe end point defining an inner edge beam. The inner and outer edgebeams limit a light bundle, which is reflected on the first opticalsurface of the mirror shell and which runs through the collector fromthe object-side aperture to a region to be illuminated in a plane. Thelight bundle defines a used region between two adjacent mirror shells.

Furthermore, the present invention also provides an illumination systemhaving such a collector, a projection exposure facility having anillumination system according to the present invention, and a method ofexposing microstructures.

Nested collectors for wavelengths ≦193 nm, particularly wavelengths inthe range of x-rays, are known from many publications.

Thus, for example, U.S. Pat. No. 5,768,339 discloses a collimator forx-rays, the collimator having a plurality of nested paraboloidreflectors. The collimator according to U.S. Pat. No. 5,768,339 is usedfor the purpose of shaping a beam bundle emitted isotropically from anX-ray light source into a parallel beam bundle.

A nested collector for X-rays is known from U.S. Pat. No. 1,865,441,which, as in the case of U.S. Pat. No. 5,768,339, is used for thepurpose of collimating isotropic X-rays emitted from a source into aparallel beam bundle.

U.S. Pat. No. 5,763,930 discloses a nested collector for a pinch plasmalight source, which is used for the purpose of collecting the radiationemitted from the light source and bundling it into a light pipe.

U.S. Pat. No. 5,745,547 discloses multiple arrangements ofmultiple-channel optics, which are used for the purpose of bundling theradiation of a source, particularly X-rays, into a point throughmultiple reflections.

In order to achieve particularly high transmission efficiency, theinvention according to U.S. Pat. No. 5,745,547 suggests ellipticalreflectors.

An arrangement for use in X-ray lithography systems, which has nestedmirrors positioned parabolically between the X-ray source and the mask,is known from German Patent 30 01 059 C2. These mirrors are positionedin such a way that the diverging X-rays are shaped into an output beambundle which runs in parallel.

The arrangement according to German Patent 30 01 059 is again used onlyfor the purpose of achieving good collimation for X-ray lithography.

The arrangement of nested reflectors known from WO 99/27542 is used, inan X-ray proximity lithography system, for the purpose of refocusinglight of a light source so that a virtual light source is formed. Thenested shells may be ellipsoidal.

A nested reflector for high-energy photon sources is known from U.S.Pat. No. 6,064,072, which is used for the purpose of shaping thediverging X-rays into a beam bundle which runs in parallel.

WO 00/63922 discloses a nested collector which is used for the purposeof collimating a neutron beam.

A nested collector for x-rays is known from WO 01/08162, which ischaracterized by a surface roughness of the inner, reflecting surface ofthe individual mirror shells of less than 12 Årms. The collectorsdisclosed in WO 01/08162 also include systems having multiplereflections, particularly Wolter systems, and is characterized by highresolution, as is required for X-ray lithography, for example.

For illumination optics for EUV lithography, as in German Patent 199 03807 or WO 99/57732, for example, in addition to the resolution, highrequirements are also necessary with regard to uniformity andtelecentricity. In systems of this type, the light of a specific lightsource is collected by a collector.

The object of the present invention is to specify a collector for anillumination system for microlithography using wavelengths ≦193 nm,preferably <126 nm, particularly preferably for wavelengths in the EUVrange, which meets the high requirements for uniformity andtelecentricity necessary for illumination optics and particularly allowsthe installation of further components, such as decoupling mirrors,detectors, or elements without optical effect, such as shieldingdevices, cooling devices, detection devices, or attachment devices,where by the homogeneous illumination in an image plane to remainuninfluenced as much as possible.

This object is achieved according to the present invention by acollector having an object-side aperture which receives light emitted bya light source and all other features of Claim 1. The collectoraccording to the present invention comprises a plurality of rotationallysymmetric mirror shells which are positioned one inside another around acommon axis of rotation. One ring aperture element of the object-sideaperture is assigned to each mirror shell. The sizes of the mirrorshells in the direction of the axis of rotation and the surfaceparameters and the positions of the mirror shells are selected in such away that an unused region is formed between two adjacent mirror shells,an outer mirror shell and an inner mirror shell. In the presentapplication, an unused region is understood as the region between twomirror shells, an inner and an outer mirror shell, which is not used bya light bundle passing through the collector from the object side to theimage plane. The unused region is typically on the back, i.e., thenon-reflecting side, of the inner mirror shell. Inner mirror shell isunderstood as the mirror shell which has the smaller distance to theaxis of rotation of the two mirror shells, the inner and outer mirrorshells.

Cooling devices, which are to be used for the purpose of preventingheating of the mirror shells due to the incident radiation, which ispartially absorbed, are preferably positioned in the unused region. Theheat load on the individual mirrors may be up to 200 K. By arranging thecooling devices in the unused region between two mirror shells, anadditional light loss, which may occur due to the introduction of thecooling devices, may be avoided. The illumination in the plane to beilluminated is therefore not impaired by shadows of the cooling devices.In a preferred embodiment of the present invention, the region to beilluminated includes a plane made of ring elements and a ring apertureelement is assigned to each ring element and the size of the mirrorshells in the direction of the axis of rotation, their surfaceparameters, and their position are selected in such a way that theirradiances of the individual ring elements in the plane correspond toeach other as far as possible.

The inventors have recognized that by the design of a nested collectoraccording to the present invention, largely uniform illumination may beachieved in a region of a plane. It is especially preferable if themirror shells are annular segments of an ellipsoid, a paraboloid, or ahyperboloid. A completely parallel beam bundle and therefore a lightsource which lies in the infinite results for a paraboloid. If, forexample, one wishes to produce secondary light sources with the aid of afirst optical element, positioned in the plane to be illuminated, havingfirst raster elements according to U.S. Pat. No. 6,198,793 B1, thecontent of whose disclosure is included in its entirety in the presentapplication, then for mirror shells which are implemented as annularsegments of a paraboloid, the individual raster elements must have acollecting effect.

The collecting effect may also be transferred to the collector. Acollector of this type according to the present invention would includeshells which are sections of ellipsoids, so that a convergent beambundle is provided. By transferring the collecting effect to a collectorwhich includes shells which are sections of ellipsoids, the first rasterelements of the first optical element may be planar facets, for example.

Collectors having shells which are sections of hyperboloids lead to adiverging beam bundle and are particularly of interest if the collectoris to be dimensioned as small as possible.

In contrast to the nested collectors according to the state of the art,the collector according to the present invention is distinguished inthat the sizes of the reflectors of the different shells are differentin the direction of the axis of rotation. In this way, largelyhomogeneous illumination may be provided in an annular region of theplane to be illuminated. If the dimensions and intervals of thereflectors are essentially identical, as in the related art cited in theintroduction, a collimated beam and/or a focused beam may be achieved,for example, but homogeneous illumination in an annular region may not.In addition, the reflection losses, which are a function of the angle,may be compensated for through suitable layout of the collector, so thatthere is homogeneous illumination in the plane.

In a preferred embodiment of the collector according to the presentinvention, the position of an outer mirror shell is further away fromthe plane to be illuminated than the position of an inner mirror shell.In this case, the position of a mirror shell is understood as theaverage of the starting point and end point of a shell in relation tothe axis of rotation of the collector. Inner mirror shell is understoodas the mirror shell which has the smaller distance to the axis ofrotation of the two mirror shells, the inner and outer mirror shells.

Since homogenization is only achieved in a discrete approximation evenusing the nested collectors, it is advantageous if the collectorincludes as many shells as possible. The collector according to thepresent invention preferably has more than four, especially preferablymore than seven, and particularly preferably more than ten reflectors ina shell-shaped arrangement.

For an isotopically emitting light source, the collector according tothe present invention ensures that identical angular segments are imagedon identical areas. In addition, the reflection losses, which are afunction of the angle, may be compensated for through suitable layout ofthe collector, so that there is homogeneous illumination in the plane tobe illuminated.

For homogeneous illumination in the plane to be illuminated, it isespecially advantageous if the ring elements adjoin one anothercontinuously. Homogeneous illumination in the plane is achieved even ifthe ring aperture elements assigned to the ring elements do not adjoinone another continuously, but have gaps. Further components, such asdevices without optical effect, particularly cooling devices, mayespecially preferably be positioned in these gaps without light lossoccurring in the plane to be illuminated.

If there is a non-isotropic source, the emission characteristic may beconverted into homogeneous illumination by the collector.

In a preferred embodiment, the radial sizes of at least two ringelements are equally large and the size in the direction of the axis ofrotation of the mirror shell of the collector assigned to the inner ringelement is larger than the size in the direction of the axis of rotationof the mirror shell of the collector assigned to the outer ring element.Inner ring element is understood as the ring element which has thesmaller distance to the axis of rotation of the two ring elements, theinner and outer ring elements.

The collector according to the present invention is advantageouslydesigned in such a way that the quotient of a first ratio of the radialsize of a first ring element to the angular size of the assigned ringaperture element and a second ratio of the radial size of a second ringaperture element to the angular size of the assigned ring apertureelement is equal to the quotient of a first radiant intensity, whichflows in the first ring aperture element, and a second radiantintensity, which flows in the second ring aperture element, i.e., thefollowing equation is true:

${\frac{\mathbb{d}A_{1}}{\mathbb{d}\Omega_{1}} \div \frac{\mathbb{d}A_{2}}{\mathbb{d}\Omega_{2}}} = {{I( \alpha_{1} )} \div ( \alpha_{2} )}$

In an alternative embodiment of the present invention, the nested mirrorshells are implemented in such a way that multiple reflections occur onone mirror shell.

Through multiple reflections on one shell, the reflection angle may bekept small.

For reflection with grazing incidence having small angles of incidenceof less than 20° relative to the surface tangents for materials such asmolybdenum, niobium, ruthenium, rhodium, palladium, or gold, thereflectivity is nearly linear to the angle of incidence relative to thesurface tangent, so that reflection losses for a reflection at 16°, forexample, or two reflections at 8° are approximately the same. However,for the maximum achievable aperture of the collector, it is advantageousto use more than one reflection.

Systems having two reflections are especially preferred. Collectorshaving two reflections may, for example, be implemented as nested Woltersystems having first mirror shells which are annular sections ofhyperboloids and second mirror shells which are annular sections ofellipsoids.

Wolter systems are known from the literature, from Wolter, Annalen derPhysik [Annals of Physics] 10, 94-114, 1952, for example. In regard toWolter systems having a real focal distance, i.e., a real intermediateimage of the source, which is formed by the combination of a hyperboloidsurface with an ellipsoid surface, reference is made to J. Optics, Vol.15, 270-280, 1984.

A special advantage of Wolter systems is that in a Wolter systems havingtwo reflections with angles of incidence less than 20° relative to thesurface tangents, a maximum collection aperture of up to NA_(max) 0.95,corresponding to an aperture angle of 80°, may be selected, while stillbeing located in the highly reflective region of the reflection having areflectivity >70%, with grazing incidence.

In a first embodiment of the present invention, the first annularsegment and the second annular segment of a shell do not adjoin oneanother continuously, but rather an unused region of the mirror shell, agap, lies between the first and second annular segments.

Further components, particularly elements without optical effect,particularly cooling devices, are preferably positioned in the unusedregion of the mirror shell of a two-shell system.

Even if these further components are positioned in the unused regionbetween two segments, additional light losses may be avoided.

It is preferable if the individual shells of a nested collector areconnected to one another by support devices. Support devices of thistype may, for example, include radially running support spokes. Supplyand removal devices for supplying coolant to and removing coolant fromthe cooling devices may be provided in the region of the radiallyrunning support spokes. The cooling devices then preferably includecooling channels. Especially good heat dissipation is achieved if thecooling devices are positioned as annular cooling plates in the unusedregion between two collector shells. The annular plate may includecooling lines. The cooling lines may be guided outward in the shadows ofthe ribs of the support devices. In a preferred embodiment, the platesmay be physically connected to the mirror shells through galvanicdeposition, for example. The heat is then removed via thermalconduction. As an alternative to this, the cooling plates may also onlybe laid on the mirror shells. This is particularly advantageous ifdeformation would occur between the cooling devices and the mirror shelldue to thermal expansion. The heat is then removed not via thermalconduction, but rather via radiation. The annular cooling plates havethe advantage of cooling over a large area, which is thereforeeffective. Furthermore, rotationally symmetric homogeneous cooling isachieved through an arrangement of this type. The optical quality isinfluenced only very slightly by a cooling arrangement of this type.

In addition to the collector, the present invention also provides anillumination system having a collector of this type. The illuminationsystem is preferably a double-faceted illumination system having a firstoptical element having first raster elements and a second opticalelement having second raster elements, as disclosed a U.S. Pat. No.6,198,793, the content of whose disclosure is included in its entiretyin the present application.

The first and/or second raster elements may be flat facets or facetswith a collecting or scattering effect.

In one embodiment of the present invention, only one annular region isilluminated on the first optical element having first raster elements.The first raster elements are then preferably positioned inside theannular region.

The illumination system which includes the collector according to thepresent invention is preferably used in a projection exposure system formicrolithography, a projection exposure system of this type beingdisclosed in PCT/EP/00/07258, the content of whose disclosure isincluded in its entirety in the present application. Projection exposuresystems include a projection objective positioned downstream from theillumination device, for example, a 4-mirror projection objective asdisclosed in U.S. Pat. No. 6,244,717, the content of whose disclosure isincluded in its entirety in the present application.

The present invention will be described in the following for exemplarypurposes on the basis of the drawing.

FIG. 1 shows a schematic sketch of a collector

FIG. 2 shows a sketch of the ring aperture element around a light source

FIG. 3 shows a sketch of the ring elements in the plane

FIG. 4 shows a nested collector made of ellipsoid segments

FIG. 5 shows a nested collector made of ellipsoid segments having adifferent number of shells than in FIG. 4,

FIG. 6 shows a refractive nested collector

FIG. 7 shows the ith elliptical segment of a nested collector

FIG. 8 shows the family of ellipses of a nested collector according tothe exemplary embodiment in Table 1

FIG. 9 shows the imaging scale β of the exemplary embodiment shown inTable 1 as a function of the image aperture angle

FIG. 10 shows the imaging scale β of the exemplary embodiment shown inTable 1 as a function of the radius r in the plane 7 in the x direction

FIG. 11 shows a projection exposure facility having a nested collectoraccording to the present invention

FIG. 12 shows the illumination distribution (irradiance) of the ringelements in the plane of the first raster elements of the projectionexposure system shown in FIG. 11 as a function of the radial distance tothe axis of rotation z of the system

FIG. 13 shows a projection exposure system having an intermediate imagehaving a nested collector

FIG. 14 shows the imaging scale β of an 8-shell nested Wolter systemaccording to FIG. 17

FIG. 15 shows a partial illustration of three shells from a nestedWolter system

FIG. 16 shows a partial illustration of two shells from a nested Woltersystem

FIG. 17 shows an 8-shell nested Wolter system

FIG. 18 shows a sketch to explain the coordinates of a collector shell,implemented as a Wolter system having two reflections

FIG. 19 shows the illumination distribution (irradiance) of the ringelements in the plane of the first raster elements of a system as shownin FIG. 20 having a collector as shown in FIG. 17

FIG. 20 shows an EUV projection exposure system having a nestedcollector as shown in FIG. 17

FIG. 21 shows coordinate systems of all mirrors of the EUV projectionexposure system shown in FIG. 20 having the nested collector shown inFIG. 17

FIG. 22 shows a first optical element of an illumination system as shownin FIG. 20 having first raster elements

FIG. 23 shows a second optical element of an illumination system asshown in FIG. 20 having second raster elements

FIG. 24 shows a 2-shell nested Wolter system having cooling devices

FIG. 25 shows a 2-shell nested ellipsoid collector having coolingdevices

FIG. 26 shows cooling rings having a support structure.

In the present application, the photometric terms listed in thefollowing table, according to Naumann/Schröder, “Bauelemente der Optik[Components of Optics]”, Hauser-Verlag, 1992, pp. 28-29, are used.

TABLE 1 Photometric terms Physical dimension Formula Unit Radiant fluxΦ_(e) $\phi_{E} = \frac{\partial Q}{\partial t}$ Watt [W] Irradiance orflux densityE_(e)$E_{e} = \frac{\mathbb{d}\;\phi_{e}}{\mathbb{d}\;{Ao}}$ Watt/cm² Radiantintensity I_(e) $I_{e} = \frac{\mathbb{d}\phi_{e}}{\mathbb{d}\;\Omega}$Watt/steradian Radiance L_(e)$L_{e} = \frac{\mathbb{d}\;\phi_{e}}{{{\mathbb{d}A_{s}} \cdot \cos}\;\alpha\; d\;\Omega}$Watt/cm²/steradian

A schematic sketch of a system having light source 1, collector 3,source image 5, and intermediate plane 7 is shown in FIG. 1. The lightsource 1 emits into the space with a specific radiant intensity. This isgenerally a function of angles α and φ (angles around the z-axis, notshown): I(α φ).

The following equation applies for axially symmetric light sources: I(αφ)=I(α).

The collector 3 collects the emitted light and bundles it. It images thelight source 1, into the light source image 5. Light source image 5 canbe either real—as shown in FIG. 1—or virtual. The light source 1 mayalso already be an image of a physical light source. In both cases, aspecific illumination 9 is obtained in a plane 7 behind the collector 3,which corresponds to the projection of the radiant intensity of the coneof radiation 11, i.e., the spatial angular element in the angle α′ inthe image space of the collector.

If the illumination is homogenized in a plane 7, it is alsoautomatically homogenized in any other plane behind the collector, if itis at a sufficient distance from the image plane in which the image 5 ofthe light source 1 lies. An associated cone of radiation 13 in theobject space, which is filled with the emitted source radiant intensityI(α) in the spatial angular element in the angle α, corresponds to thecone of radiation 11 in the image space.

According to the present invention, any arbitrary light source 1 isimaged in an image of the source. The source image may be real (i.e., tothe right of the collector 3 in the light direction) or virtual (i.e.,to the left of the collector 3 in the light direction), or may lie inthe infinite.

In a preferred embodiment of the present invention, the emissioncharacteristic of any arbitrary light source 1 is transformed in such away that a largely homogeneous illumination results in a plane in frontof or behind the intermediate image.

According to the present invention, the following equation is to apply:

$\begin{matrix}{E = {\frac{\phi}{\mathbb{d}A} = {\frac{{R(\alpha)}I*(\alpha){\mathbb{d}\Omega}}{\mathbb{d}A} = {{const}.}}}} & (2.1)\end{matrix}$

E: irradiance in the plane 7

φ: radiant flux

dA: surface element in plane 7

dΩ: angular element in the object-side aperture

I*(α): radiant intensity of the source at the angle

R (α): attenuation factor proportional to light losses through thefinite reflectivity of the collector, which is a function of the angle(in the following, I(α)=R(α)×I*(α) is used without restrictinggenerality)

Therefore, the following equation must apply for two ring elementshaving equal irradiance:

$\begin{matrix}{E = {\frac{\phi_{1}}{\mathbb{d}A_{1}} = {\frac{{I( \alpha_{1} )}{\mathbb{d}\Omega_{1}}}{\mathbb{d}A_{1}} = {\frac{\phi_{2}}{\mathbb{d}A_{2}} = \frac{{I( \alpha_{2} )}{\mathbb{d}\Omega_{2}}}{\mathbb{d}A_{2}}}}}} & (2.2)\end{matrix}$from which the following equation results:

$\begin{matrix}{{\frac{\mathbb{d}\Omega_{2}}{\mathbb{d}A_{2}} \div \frac{\mathbb{d}\Omega_{1}}{\mathbb{d}A_{1}}} = {{I( \alpha_{1} )} \div {I( \alpha_{2} )}}} & (2.3)\end{matrix}$

For anisotropic sources or strong differences in the reflection lossesR(α), the ring aperture segments and/or ring elements in plane 7 must beselected in accordance with equation (2.3).

In general, the object of producing an intermediate image andsimultaneously adjusting an emission characteristic may not be fulfilledusing simple optical elements such as a mirror or a lens. Forrotationally symmetric emission characteristics around the z-axis, whichis identical to the optical axis of the system in the present case,uniform illumination may be achieved via a special type of Fresneloptic, at least for discrete regions.

This is explained in the following using the example of a realintermediate image of the source 1. For virtual intermediate images orsource images in the infinite, similar constructions result in anobvious way for one skilled in the art.

Three angular segments and/or ring aperture elements 20, 22, 24, forexample, as shown in FIG. 2, are selected around the source 1. Theradiant flux through the ring aperture elements is given by:

$\begin{matrix}{\Phi_{i} = {\int\limits_{\varphi = 0}^{2\pi}{\int\limits_{\alpha = \alpha_{i}}^{\alpha_{i + 1}}{I*( {\alpha,\varphi} ){\mathbb{d}\Omega}}}}} & ( {2.4a} )\end{matrix}$

For most of the existing rotationally symmetric sources, whose radiantintensity varies only slightly with the angle α, such as the denseplasma focus source, the radiant flux may be approximately described by:Φ_(i)≈2πI*(α_(i))·(cos α_(i)−cos α_(i+1))  (2.4b)in which

-   φ_(i): radiant flux-   I*(α_(i)): radiant intensity of the source in the angle α_(i)-   α_(i): inner angle of the ith angular segment,-   α_(i+1): outer angle of the ith segment with α_(i+1)=α_(i)+dα_(i)-   dα_(i): width of the ith angular segment

The generally differing angular increments dα_(i) are determined viaequation (2.4), so that the irradiance in the assigned ring elements inplane 7 is largely identical.

The ring aperture segments 20, 22, 24 are shown in FIG. 2. An examplehaving three segments 20, 22, 24 which lie between NA_(min) and NA_(max)is shown. The segments 22 and 24 adjoin one another. A small gap 26exists between the segments 20 and 22.

The individual ring aperture segments and/or ring aperture elements 20,22, 24 are assigned to ring elements 30, 32, 34 in the plane 7 to beilluminated, whereby the following equation generally applies:r _(i+1) =r _(i) +dr _(i)  (2.5)In which

-   r_(i): inner interval of the ith ring element in the plane 7 to be    illuminated-   r_(i+1): outer interval of the ith ring element in the plane 7 to be    illuminated-   dr_(i): height increment or radial size of the ith ring element

The ring elements 30, 32, 34 are selected, for example, in such a waythat equally large intervals dr_(i)=dr=constant are achieved between theedge beams of the ring elements. The illumination in the plane 7 usingring elements 30, 32, 34 is shown in FIG. 3.

For a ring element having largely uniform irradiance in plane 7, thefollowing equation applies for the radiant flux:

$\begin{matrix}{\Phi_{i}^{\prime} = {{2\pi{\int_{r = r_{i}}^{r_{i + 1}}{{Er}{\mathbb{d}r}}}} \approx {\pi\;{E \cdot ( {r_{i + 1}^{2} - r_{i}^{2}} )}}}} & (2.6)\end{matrix}$in which

-   φ′_(i): radiant flux through the ith ring element in the plane 7 to    be illuminated

Taking the reflection losses on the ith collector shell R′(α) intoconsideration, the width dα_(i) of the ith ring aperture elements andthe radial size dr_(i) of the ith ring segment may thus be determined.For example, the radial size dr selected may be constant. WithΦ′_(i) =R′(α_(i))Φ_(i)  (2.7)and the requirement for largely uniform irradiance E

$\begin{matrix}{E = {\frac{\Phi_{i}^{\prime}}{\pi \cdot ( {r_{i + 1}^{2} - r_{i}^{2}} )} = {{const}.}}} & (2.8)\end{matrix}$the following equation results after using equation (2.4) and solvingfor α_(i+1):

$\begin{matrix}{\alpha_{i + 1} = {\arccos\lbrack {{\cos\;\alpha_{i}} - {E\frac{( {r_{i + 1}^{2} - r_{i}^{2}} )}{2{{I( \alpha_{i} )} \cdot {R^{\prime}( \alpha_{i} )}}}}} \rbrack}} & (2.9)\end{matrix}$in which

-   E: largely uniform irradiance in the plane 7 to be illuminated-   r_(i): inner interval of the ith ring element in the plane 7 to be    illuminated-   r_(i+1): outer interval of the ith ring element in the plane 7 to be    illuminated-   α_(i): inner angle of the ith ring aperture element,-   α_(i+1): outer angle of the ith ring aperture element.

If the ring elements in plane 7 are selected via equation (2.5), theangle of the ring aperture elements may be determined according toequation (2.9).

The edge beams of the ring elements and/or of the ring aperture elementsare thus located.

Via the points of intersection of selected beams, the particularelliptical shells of the collector 3 are then located. For a virtualintermediate image, these are hyperboloid, for a source image in theinfinite, they are paraboloid. A representative beam is selected in eachring aperture element 20, 22, 24 for this purpose.

For an ellipsoid and/or hyperboloid or paraboloid shell, it issufficient to specify object point and image point, source 1 and source5 in this case, and only one further point. In the present case,however, two points, specifically a starting point and an end point ofthe collector shell, are given, i.e., the problem is overdefined. Since,however, the imaging quality for the source imaging may typically belargely ignored for illumination purposes, the ellipses and/orhyperbolas or parabolas may, for example, have a conical component inthe shape of a wedge or truncated cone added, which corresponds to aslight defocusing, which does not come into consideration.Alternatively, slight shadowing is accepted, since the gaps occurringmay be selected to be very small. The size of the gaps may be minimizedvia the layout and particularly the number of shells. The gaps areselected, for example, in such a way that they occur at the front, i.e.,in the absorbed output from the source, and not behind, in the area tobe illuminated.

It is also possible to construct the collector only from truncatedcones, particularly if the collector includes multiple shells. This isadvantageous from a manufacturing viewpoint.

If the shadows are ignored, it is then ensured that an equal radiantflux results both through the angular segments and/or ring apertureelements 20 to 24 and through the area segments and/or ring elements 30to 34.

In principle, it is also possible to compensate for the reflectionlosses as a function of angle, and therefore as a function of thesegment by suitable derivative action in the angle increments α_(i),whereby since one wishes to illuminate the area 7 largely homogeneouslyaccording to the present invention, the ring aperture segments, whichare assigned to ring segments having identical increments, not beingidentically large. Alternatively, the height increments dr of the ringelements may also be selected to be of different size.

A nested collector 3 is shown in FIG. 4, made of ellipsoid segmentswhich are positioned rotationally symmetrically around the z-axis, whichensures a largely equipartitioned illumination of the plane 7. Due tothe rotational symmetry around the z-axis, only one half of thecollector 3 is shown in section. The collector shown in FIG. 4 includesfour shells 40, 42, 44, and 46.

The shells 40, 42, 44, and 46 are positioned approximately equidistantfrom the z-axis, in regard to the maximum shell diameter, which isapproximately proportional to the shell number i, i.e., the spacing oftwo adjacent shells is approximately equal.

Each mirror shell 40, 42, 44, 46 is assigned an inner edge beam 41.1,43.1, 45.1, 47.1, which is given by the end point of the optical surfaceof the mirror shell, and an outer edge beam 41.2, 43.2, 45.2, 47.2,which is determined by the starting point of the optical surface of themirror shell. As may be clearly seen in FIG. 4, the inner and outer edgebeams of each mirror shell define a beam bundle 49.1, 49.2, 49.3, 49.4assigned to this mirror shell, which is reflected on the opticalsurfaces of the mirror shells 40, 42, 44, 46 in the direction of theimage source. Optical surface(s) of a mirror shell is/are understood inthe present application as the area(s) of the mirror shell whichreceive(s) the beam bundle incident from the light source 1 andreflect(s) it in the direction of the image 5 of the light source. Theincident beam bundle and the beam bundle reflected on the opticalsurfaces of the mirror shells define a region used by the light betweentwo neighboring or adjacent mirror shells. It may also be clearly seenthat an unused region 51.1, 51.2, 51.3, 51.4 is provided on the side ofthe adjacent mirror shell facing away from the optical surfaces, inwhich components without optical effect, such as cooling devices, may bepositioned, for example. The advantage of positioning cooling devices,for example, in these unused regions is that they allow cooling withoutadditional loss of light.

Furthermore, the light source 1, the plane 7 to be illuminated, and thesource image 5 are shown in FIG. 4.

The reference numbers of the other elements correspond to those in thepreceding figures.

Alternatively, an arrangement is possible in which the length of theshells is reduced, as shown in FIG. 5. For example, the innermostangular segment and/or ring aperture element 20 may be divided into twoangular segments and/or ring aperture elements 20.1 and 20.2.Correspondingly, the assigned innermost ring element 30 in the area 7 isalso divided into two ring elements 30.1, 30.2. Two shells 40.1, 40.2then result for the two inner segments, which are shorter than one shell40, as may be clearly seen from FIG. 5. Identical components as in thepreceding figures are provided with the same reference numbers.

A similar arrangement may also be possible for refractive systems. Forrefractive systems, the nested mirror shells 40, 42, 44, 46 are replacedby annular off-axis segments of lenses 50, 52, 54, 56, as shown in FIG.6.

FIG. 6 schematically shows an arrangement of annular off-axis segmentsof lenses, which results in equipartitioned illumination of the plane 7for a specific emission characteristic of the source. Only half of thesystem, which is rotationally symmetric around the z-axis, isschematically shown in section. Angular elements of different sizes arereflected on height segments of equal sizes and homogeneous illuminationis therefore achieved even in the event of anisotropic source emission.

Nested, reflective collectors necessarily have a central shadowing,i.e., below a specific aperture angle NA_(min), the emission of thesource may not be absorbed. This radiation must therefore be blocked bya diaphragm, so that light may not reach the illumination system. Thediaphragm may, for example, be attached in the collector.

In the following, the present invention is to be described in greaterdetail on the basis of an exemplary embodiment.

Point-to-point imaging having a real source image for an isotropicsource with a family of ellipses corresponding to the present inventionis assumed, the intervals of adjacent mirror shells being selected to beapproximately equal.

An ellipse is defined according to the equation

$\begin{matrix}{{{\frac{z^{2}}{\alpha^{2}} + \frac{x^{2}}{b^{2}}} = 1}{with}} & (3.1) \\{c = {\sqrt{a^{2} - b^{2}}.}} & (3.2)\end{matrix}$

The ith ellipse segment is shown in FIG. 7 for exemplary purposes. Sincethis is rotationally symmetric around the z-axis, only one half is shownin section.

The dimensions used for the calculation according to Table 1 are shownfor a mirror shell in FIG. 7. The same reference numbers as in thepreceding figures are used for identical components.

-   v(i) indicates the ith starting point of the ith mirror shell-   x(v(i)) indicates the x coordinate of the ith starting point-   z(v(i)) indicates the z coordinate of the ith starting point, i.e.,    the starting point in relation to the axis of rotation RA-   h(i) indicates the ith end point of the ith mirror shell-   x(h(i)) indicates the x coordinate of the ith end point-   z(h(i)) indicates the z coordinate of the ith end point, i.e., the    end point in relation to the axis of rotation RA-   m(i) indicates the average value of the starting and end points of    the ith shell-   x(m(i)) indicates the x coordinate of the average value-   z(m(i)) indicates the z coordinate of the average value, i.e., the    average value of the starting and end points of the ith shell in    relation to the axis of rotation RA-   a, b indicates parameters of the ellipse-   r(i) indicates the distance of the ith ring element of the ith shell    in the plane to be illuminated from the axis of rotation RA-   NA(i) indicates the sine of the aperture angle of the inner edge    beams of the ith ring aperture element of the ith shell

FIG. 8 shows the family of ellipses of the shells 60, 62, 64, 66, 68,70, 72, 74, 76, 80 resulting for the exemplary embodiment calculatedusing the parameters defined above. In the present exemplary embodiment,both equally large angular increments dα and equally large heightincrements dr were selected. This is possible with isotropic sources andsmall apertures, particularly if the irradiance is to be onlyapproximately equal. The data is indicated in Table 2. All lengths inTable 2 are indicated in mm. All angles of incidence relative to thesurface tangents are below 19°. The angle of incidence relative to thesurface tangent of the maximum beam in the exemplary embodimentaccording to FIG. 8 is 18.54°.

The following values were selected as starting values:

Distance between plane 7 and source image 5:

z=900 mm

Half focal point distance:

e=1000 mm

Height increment on surface 7:

dr=7.5 mm

Central shadowing in surface 7:

r_(min)˜22.5 mm (NA′_(min)˜0.025)

Minimum aperture NA_(min) for source 1:

NA_(min)=0.12

Maximum aperture NA_(max) for light received by the collector

NA_(max)<0.55, corresponding to 33°

Angular increments at source 1:

dα_(i)=2.4°=const.

TABLE 2 Parameters of the family of ellipses Ref. i no. r(i) NA(i) a bx(h(i)) z(h(i)) x(v(i)) z(v(i)) 1 60 22.507 0.120 1002.009 63.422 52.266−567.601 43.117 −734.837 2 62 30.007 0.161 1003.391 82.423 66.429−593.993 57.195 −722.489 3 64 37.507 0.203 1005.130 101.423 80.551−610.765 71.258 −715.251 4 66 45.007 0.243 1007.231 120.475 94.679−622.848 85.334 −710.997 5 68 52.507 0.284 1009.699 139.612 108.838−632.382 99.443 −708.705 6 70 60.007 0.324 1012.540 158.863 123.046−640.449 113.597 −707.824 7 72 67.507 0.363 1015.762 178.250 137.317−647.655 127.810 −708.034 8 74 75.007 0.402 1019.374 197.798 151.664−654.371 142.092 −709.139 9 76 82.507 0.440 1023.386 217.529 165.097−660.836 156.455 −711.012 10 78 90.007 0.477 1027.808 237.466 180.628−667.215 170.909 −713.571 11 80 97.507 0.513 1032.654 257.632 195.269−673.626 185.464 −716.763

In FIG. 9, the imaging scale β of the exemplary embodiment shown in FIG.8 and Table 2 is shown as the measure of the homogeneity of theillumination as a function of the image aperture angle. The imagingscale β does not have to be constant over the angle, but a specificimaging scale must result over the maximum radius r_(max) in plane 7.

In FIG. 10, the ideal imaging scale β-ideal and the real imaging scale βare shown as a function of the radius r in the plane 7 by discretedsolution of the collimation problem. The deviation from the idealimaging scale may be reduced by increasing the number of shells, bysplitting the inner shells into two shells each, for example, as shownin FIG. 5. In this way, even better homogenization of the illuminationmay be achieved in area 7.

A schematic view of a projection exposure apperatus, for the productionof microelectronic components, for example, in which the presentinvention may be used, is shown in FIG. 11. The projection exposureapparatus includes a light source or an intermediate image of a lightsource 1. The light emitted by the light source 1, of which only fourrepresentative beams are shown, is collected by a nested collector 3according to the present invention and deflected on a mirror 102 havingmultiple first raster elements, or field honeycombs. In the presentcase, the first raster elements are planar. The mirror 102 is alsoreferred to as a field honeycomb mirror. The illumination in the plane103, in which the field honeycomb mirror is positioned, is largelyhomogeneous in a predetermined annular region, as shown in FIG. 12. Theplane 103 is not exactly perpendicular to the optical axis of thecollector and therefore does not exactly correspond to the homogerieousplane 7 to be illuminated from FIG. 1. However, a slight angle ofinclination does not change the derivation and only leads to slightdistortions of the illumination and therefore to a deviation fromhomogeneity, as would exist in a plane perpendicular to the optical axisof the collector, which may be ignored. The illumination system is adouble-faceted illumination system as disclosed in U.S. Pat. No.6,198,793 B1, whose content is included in its entirety in the presentapplication. The system therefore includes a second optical elementshaving raster elements 104, which are referred to as pupil honeycombs.The optical elements 106, 108, and 110 are essentially used for thepurpose of shaping the field in the object plane 114. The reticle in theobject plane is a reflection mask. The reticle is movable in the EUVprojection system, which is e. g. a scanning system, in the direction116 shown. The exit pupil of the illumination system is illuminatedlargely homogeneously. The exit pupil is coincident with the entrancepupil of a projection objective which is situated in the light path fromthe light source to the object 124 to be illuminated after theillumination system; i. e. downstream of the illumination system. Theentrance pupil of the projection objective is not shown. The entrancepupil is given by the point of intersection of the chief ray for e. g.the central field point of the field in the object plane of theillumination system with the optical axis of the projection objective.

A projection objective 126 having six mirrors 128.1, 128.2, 128.3,128.4, 128.5, 128.6, for example, according to U.S. patent applicationSer. No. 09/503640, forms the reticle on the object 124 to beilluminated.

FIG. 12 shows the illumination distribution in the plane of the firstoptical element having first raster elements and the average value ofthe illumination. The irradiance E(r) is shown as a function of theradial distance r from the axis of rotation z of the nested collector.It may be seen clearly that the fulfillment of homogenized illuminationis only discrete.

A schematic sketch of an EUV projection exposure apparatus is shown inFIG. 13, which differs from the apparatus shown in FIG. 11 only in thatthe light source 1 is imaged into an intermediate image Z. In addition,the first raster elements now have a collecting effect. The intermediateimage Z of the light source 1 is implemented between collector 3 and thefirst faceted mirror 102. All of the other components are identical tothe components shown in FIG. 11 and therefore have the same referencenumbers.

Nested collectors according to the present invention, which areimplemented as Wolter systems, are shown in the following FIGS. 14 to21.

A Wolter system, preferably made of a combination of a hyperboloid andan ellipsoid for the real imaging of the light source 1 in anintermediate image Z of the source, but also a hyperboloid-paraboloidfor imaging to infinity, is characterized by largely fulfilling the sinecondition, i.e., the enlargement and/or the imaging scale of acombination of hyperboloid and ellipsoid is largely constant over alarge aperture range. As shown in FIG. 9, the imaging scale β within theshell varies strong in a collector for homogenized illumination havingonly simple ellipsoid shells. In a Wolter system, in contrast, theimaging scale β inside the shell is largely constant. This is shown inFIG. 14 for an 8-shell nested system as shown in FIG. 17, in which eachindividual one of the nested mirror shells is a Wolter system, having afirst annular segment having a first optical surface, which is a sectionof a hyperboloid, and a second annular segment having a second opticalsurface, which is a section of an ellipsoid. Wolter systems thereforehave two optical surfaces per shell, a first and a second opticalsurface, in contrast to the systems having simple ellipsoid shells.These surfaces may also be mechanically separated from one another.

Since, as shown in FIG. 14, a shell of a Wolter system has a nearlyconstant imaging scale β, it is necessary, to achieve ideal homogenizedillumination of a plane, that gaps arise in the object-side aperture.This is particularly true because in the event of grazing incidence, thereflectivity on the shells which have the greatest distance to the axisof rotation is lower than for shells which have the smallest distance tothe axis of rotation. Molybdenum, niobium, ruthenium, rhodium,palladium, or gold are preferably considered as mirror materials. Thismust be compensated for through increasing imaging scale. The imagingscale must then be changed from shell to shell for homogeneousillumination. If, at the same time, one wishes to achieve continuousfilling of the aperture after the collector and/or continuousillumination of the area 7 behind the nested collector, gaps arise inthe object-side aperture. This is not the case in a collector havingellipsoidal shells, for example, as described in FIGS. 1 to 13, sincethen the imaging scale varies over the shells and thus, in addition tothe homogenized, continuous illumination of a plane 7, a continuousobject-side aperture may also be achieved.

In FIG. 15, three shells of a nested collector according to the presentinvention are shown as examples, each mirror shell 200, 202, and 204having a Wolter system having a first annular segment 200.1, 202.1,204.1, which has a first optical surface 200.2, 202.2, 204.2, and asecond annular segment 200.3, 202.3, 204.3, which has a second opticalsurface 200.4, 202.4, 204.4. The individual shells 200, 202, 204 arepositioned rotationally symmetrically around the z-axis. The imagingscale β of the innermost shell 204 is 6.7, that of the second shell 202is 7.0, and that of the outermost shell 200 is 7.5. As may be seen fromFIG. 15, the ring aperture elements 210, 212, 214, which are assigned tothe particular mirror shells 200, 202, and 204, do not adjoin oneanother, i.e., the object-side aperture of the collector shown in FIG.15 has gaps 220, 222, 224 between the individual ring aperture elements210, 212, 214. The ring elements 230, 232, 234 in the plane 7 assignedto the particular mirror shells 200, 202, 204 adjoin one another largelycontinuously to achieve homogeneous illumination of a region of theplane 7.

Cooling devices 203.1, 203.2, 203.3 are preferably positioned in theregion of the gaps 220, 222 of the ring aperture elements on the back ofthe mirror shells 200, 202, 204. The cooling devices are preferablycooling channels which may have a coolant flushed through them. Thecooling devices 203.1, 203.2, 203.3 extend on the back of the particularshells largely over their entire length in the direction of the axis ofrotation. An embodiment having additional components which arepositioned in an unused region of the collector between two mirrorshells is shown in greater detail and described in FIG. 25.

Each shell 200, 202, 204 is assigned an inner edge beam 205.1, 207.1,209.1, which is defined by the end point in the meridional plane of thefirst optical surface of the first segment of the mirror shell, and anouter edge beam 205.2, 207.2, 209.2, which is defined by the startingpoint in the meridional plane of the first optical surface of the firstsegment of the mirror shell. The inner and the outer edge beam determinethe beam bundle, which is received by the shell and guided to the sourceimage within two adjacent shells. The region which a beam bundle 211.1,211.2 does not pass through between two collector shells is, as alreadydescribed for the single shell collector shown in FIG. 4, referred to asan unused region 213.1, 213.2. As may be clearly seen from FIG. 15, thecooling devices positioned in the region of the gaps of the ringaperture elements on the back of the mirror shells are positioned in theunused region between two mirror shells.

In the embodiment shown in FIG. 15, the first optical surface 200.2,202.2, 204.2 and the second optical surface 200.4, 202.4, and 204.4 alsoadjoin one another directly without gaps.

A further exemplary embodiment of the present invention is shown in FIG.16, only two mirror shells 200, 202, which are designed as a Woltersystem, being illustrated for exemplary purposes. Identical componentsas in FIG. 15 are provided with the same reference numbers. In theembodiment in FIG. 16, the first optical surface 200.2, 202.2 and thesecond optical surface 200.4, 202.4 do not adjoin one another directly.There is a gap and/or an unused region 240, 242 between the opticalsurfaces. In the present exemplary embodiment, however, the mirrorshells are continued in the unused region up to the intersection S1, S2of the first and second segment 200.1, 202.1, 200.3, 202.3 of theparticular mirror shell. Both first optical surfaces 200.2, 202.2 on thefirst mirror segments are delimited in the meridional plane by startingpoints 311.1, 312.1 and end points 311.2 and 312.2. The meridional planeis given in the present application by the plane which contains theoptical axis or axis of rotation. Starting and end points 311.1, 312.1,311.2, 312.2 of the optical surfaces define edge beams 205.1, 205.2,207.1, and 207.2, which, when rotated around the axis of rotation,define a light bundle which is passed through the collector, i.e., runsthrough the collector from the object side to the image side. The lightbundle passed through the collector in turn defines the used region ofthe collector.

As shown in FIG. 16, a cooling device, for example, a cooling shieldrunning around the entire circumference of the mirror shell, may bepositioned in the region of the gaps 240, 242. The cooling shields maybe mechanically supported by ribs running in the direction of the axisof rotation, as shown in FIG. 26. For good thermal contact, the ribs aresoldered to the peripheral cooling shields, for example. The supportelements for the cooling shields, which run in the direction of the axisof rotation, may be attached to the support structures which support themirror shells, spoked wheels, for example. The spoked wheels and supportstructures are not shown in the present FIG. 16.

A design having gaps and/or unused regions, as shown in FIG. 16, isadvantageous for extended light sources.

Balancing between collection efficiency and homogeneity of theillumination is always to be performed in the design of the collector.If one wishes to achieve a homogeneity of only ±15% in the surface 7 tobe illuminated, an 8-shell collector, as shown in FIG. 17, may be usedfor this purpose. In this case, 200, 202, 204, 205, 206, 207, 208, 209indicate the particular mirror shells, each having two mirror segmentsand each shell representing a Wolter system.

The collector from FIG. 17 has a distance of 1500 mm between source 1and intermediate image of the source Z, an object-side aperture of ˜0.72and an image-side aperture of ˜0.115. All of the angles of incidencerelative to the surface tangents are ≦130. The angle of incidencerelative to the surface tangent of the maximum beam in the exemplaryembodiment shown in FIG. 17 is 11.90.

Furthermore, a diaphragm 180 positioned in the inside of innermostmirror shell is shown in FIG. 17. Nested, reflective collectorsnecessarily have central shadowing due to the finite size of the mirrorshells, i.e., below a minimum aperture angle NA_(min) the radiation ofthe source may not be absorbed. The diaphragm 180 prevents light passingdirectly through the central shell from reaching the illumination systemsituated in the light paten behind the inventive collector as straylight.

The diaphragm 180 is, for example, positioned 78 mm behind the sourceand has a diameter of 30.3 mm, corresponding to an aperture obscurationof NA_(obs)˜0.19. Correspondingly, the image-side aperture obscurationis NA′_(obs)˜0.0277.

The characteristic coordinates of a Wolter system, including twosegments, the first segment 200.1 and the second segment 200.3 of thefirst mirror shell 200, for example, are illustrated in FIG. 18 as anexample for the mirror shells 200, 202, 204, 205, 206, 207, 208, 209 ofthe collector shown in FIG. 17. ZS indicates the z-position of thesurface apex in relation to the position of the light source 1, ZV andZH indicate the starting and end positions of the first segment 200.1,which is a hyperboloid, in relation to the position of the surface apexZS. For the second segment 200.3 of the mirror shell, which is anellipsoid, the reference letters ZS, ZH, and ZV are used in an analogousway.

Using the curvature radii R and the conical constants K of theparticular mirror segment as well as the definitions specified, thedesign data of the collector shown in FIG. 17 from the following Table 3result. Ruthenium was selected as the coating of the mirror shells.

TABLE 3 Design data of the collector shown in FIG. 17 Shell R[mm] KZS[mm] ZV[mm] ZH[mm] Hyperboloid 1 1.5866 −1.0201 −0.79 108.99 185.86 22.3481 −1.0286 −1.17 107.92 183.90 3 3.5076 −1.0399 −1.74 107.56 182.354 5.0414 −1.0571 −2.49 105.05 179.53 5 7.2534 −1.0814 −3.56 102.83177.68 6 10.4354 −1.1182 −5.07 99.95 175.90 7 15.0523 −1.1755 −7.2294.87 173.09 8 22.3247 −1.2660 −10.50 88.88 169.39 Ellipsoid 1 2.3724−0.9971 −160.94 349.66 433.46 2 3.3366 −0.9960 −168.17 353.68 440.17 34.6059 −0.9945 −181.56 363.50 454.10 4 6.4739 −0.9923 −184.74 364.03457.33 5 9.0813 −0.9893 −189.80 366.19 463.15 6 12.8589 −0.9849 −193.20365.14 466.03 7 18.4682 −0.9783 −195.28 362.33 470.02 8 26.8093 −0.9688−202.36 362.94 480.72

The exemplary embodiment of the Wolter system shown in FIG. 17 havingeight shells is selected in such a way that all shells end approximatelyin a plane 181. In this way, all shells may be mounted in a plane 181.

The spoked wheels shown in FIG. 27, which include a total of foursupport spokes in the embodiment shown in FIG. 27, may be used as themounting of the shells and/or support of the shells. The support spokesprovide stability to the nested collector having a plurality of mirrorshells.

The diaphragm 180 is preferably positioned in or near this plane.

The illumination distribution defined in the plane 7 of the illuminationsystem shown in FIG. 20 is shown in FIG. 19. The illumination systemshown in FIG. 20 includes an 8-shell nested collector situated directlybehind the light source, as shown in FIG. 17. The calculation of theirradiance as shown in FIG. 19 was based on a ruthenium coating of themirror shells using their reflectivity, which is a function of theangle. The design of the collector may be adjusted appropriately forother coatings.

The central shadowing by the screen 180 may be seen clearly in FIG. 19.The central shadowing is indicated by the reference number 182. Theshape of the intensity in plane 7 is indicated by 184. Two peaks ofintensity 184.1, 184.2, which lead to an annular illumination in theplane 7 and which are symmetrical to the axis of rotation RA of thecollector, may be seen clearly. The dashed curve 186 indicates theregion in which first raster elements are positioned on the firstoptical element 102 of the illumination system shown in FIG. 20.

The optical components and the beam path of some light beams of aprojection exposure apparatus having a nested collector as shown in FIG.17 are shown in FIG. 20. Identical components as in the projectionexposure apparatus shown in FIG. 11 are provided with the same referencenumbers.

In contrast to the projection exposure apparatus shown in FIG. 11, theillumination system is not folded like an “X”, but is optimized forcompact installation space. To reduce the system length, the image-sideaperture of the nested collector 3, which has a construction as in FIG.17, is also increased to NA=0.115, for which the layout as a Woltersystem is especially advantageous. The object-side aperture is NA˜0.71.A planar mirror 300 for folding the system is also introduced followingthe collector 3, in order to provide installation space for mechanicaland electronic components in the object plane 114, in which the waferstage is positioned. The overall optical system is less than 3 m longand less than 1.75 m tall.

In the present embodiment, the planar mirror 300 is designed as adiffractive spectral filter, i.e., realized by a grating. Together withthe diaphragm 302 near the intermediate image Z of the source, undesiredradiation having wavelengths significantly greater than the desiredwavelength, for example, in the present case 13.5 nm, may thus be keptfrom entering the part of the illumination system behind the diaphragm302.

The diaphragm 302 may also be used for the purpose of spatiallyseparating the space 304 comprising light source 1 the nested collector3, and the planar mirror 300, designed as a grating element from thefollowing illumination system 306. If both spaces are separated byintroducing a valve near the intermediate focus Z, separation in regardto pressure is also possible. Through spatial and/or pressureseparation, contamination which arises from the light source may beprevented from reaching the illumination system behind the diaphragm302.

The illumination system shown in FIG. 20 includes a nested collector 3having 8 shells as shown in FIG. 17 and Table 3. The planar mirror 200of the design shown in FIG. 20 is implemented as a spectral filterhaving a diffractive angle of 2° between 0 and the order of diffractionused. The first optical element 102 includes 122 first raster elements,each having dimensions of 54 mm×2.75 mm. The second optical element 104has 122 second raster elements assigned to the first raster elements,each having a diameter of 10 mm. All indications of location of theoptical components in Table 4 are in relation to the referencecoordinate system in the object plane 114. The rotation around the anglea around the local x-axis of the local coordinate systems assigned tothe particular optical components results after translationaldisplacement of the reference coordinate system to the location of thelocal coordinate system. The parameters of the optical components of theillumination system shown in FIG. 20 are indicated in Table 4. In Table4, the positions of the vertices of the individual optical elements inrelation to the object plane 114 and the angle of rotation a of thecoordinate systems around the x-axis are specified. Furthermoreright-hand coordinate systems and clockwise rotation are used. Besidesthe local coordinate systems of the optical components, the localcoordinate systems of the intermediate focus and the entrance pupil areindicated. The field-shaping mirror 110 includes an extra-axial segmentof a rotational hyperboloid. The coordinate systems for all of theoptical elements of the illumination system shown in FIG. 20 anddescribed in Table 4, with the exception of the nested collector 3, areshown in FIG. 21. All of the optical elements are provided with the samereference numbers as in FIG. 20.

The system is calculated for a field radius of 130 mm with anillumination aperture of NA=0.03125 in object plane 114, i.e., on thereticle, corresponding to a filling ratio of σ=0.5 in the entrance pupilE of a downstream 4:1 projection objective having an aperture NA=0.25 inthe plane 124 of the object to be illuminated.

TABLE 4 Design data of the system shown in FIG. 20 Apex curvatureConical Position Y Z α radius constants Light source 1 2148.137−1562.205 70.862 No mirror surface Planar mirror and/or 1184.513−1227.797 147.434 Planar spectral filter 200 Intermediate focus Z883.404 −893.382 42.000 No mirror surface First faceted optical 302.599−248.333 36.000 −898.54 Spherical element 102 Second faceted 773.599−1064.129 214.250 −1090.15 Spherical optical element 104 Mirror 106126.184 −250.216 31.500 288.1 Spherical Mirror 108 372.926 −791.643209.600 −855.8 Spherical Mirror apex of mirror −227.147 118.541 −4.965−80.5 110 Object plane 114 0.000 0.000 0.000 Planar Entrance pupil E−130.000 −1236.867 0.000 No mirror surface

As in the nested collector shown in FIGS. 1 to 13, the shells of theWolter system may also be produced easily by molding technologies.

The first optical element 102 in the plane 103 of the illuminationsystem shown in FIG. 20 having a local x-y coordinate systems is shownin FIG. 22. The arrangement of the 122 first raster elements 150 isclearly shown.

The first raster elements 150 are positioned in ten blocks 152.1, 152.2,152.3, 152.4, 152.5, 152.6, 152.7, 152.8, 152.9, 152.10 at intervalsfrom one another.

No first raster elements 150 are positioned in the region in the plane103 not illuminated due to the central shadowing 154 of the collector 3.The maximum deviation of the irradiance between individual first rasterelements 150 is less than ±15% if a nested collector as shown in FIG. 17is used.

FIG. 23 shows the arrangement of the second raster elements 156 on thesecond optical element 104. The images of the second raster elements 158fill the exit pupil of the illumination system continuously up to agiven filling ratio of σ=0.5. Reference is made to WO 01/09684, thecontent of whose disclosure is included in its entirety in the presentapplication, in regard to the definition of the filling ratio in theexit pupil.

A first embodiment of a nested collector according to the presentinvention having, for example, two mirror shells 1004.1, 1004.2positioned one inside the other is shown in FIG. 24, in which the ringaperture elements, as in the nested collector shown in FIG. 15, have agap 1000 between the object-side ring aperture elements 1002.1 and1000.2 of the first mirror shell 1004.1 and the second mirror shell1004.2. The image-side ring elements 1003.1, 1003.2 adjoin one anotherdirectly, so that there is no gap in the image space except for thenecessary central shadowing 1005. In the collector shown, coolingdevices 1006.1, 1006.2, 1006.3 are positioned in the unused regionbetween the two mirror shells 1004.1, 1004.2 and inside and outside thecollector. The mirror shells 1004.1, 1004.2 end approximately in oneplane and may be mounted in this plane 1008 by a spoked wheel, forexample, of which one spoke 1010 is shown. Each mirror shell 1004.1,1004.2 of the embodiment shown includes two mirror segments, a firstmirror segment 1007.1, 1007.2 having a first optical surface and asecond mirror segment 1009.1, 1009.2 having a second optical surface,which are positioned one behind the other without gaps. The first mirrorsegments 1007.1, 1007.2 are segments of hyperboloids in the presentexemplary embodiment and the second mirror segments 1009.1, 1009.2 aresegments of ellipsoids.

As may be clearly seen in the meridian section shown in FIG. 24, theinner and outer edge beams 1016.1, 1016.2, 1018.1, 1018.2 of theparticular mirror shell and/or the connection lines assigned to thembetween the source 1, the image of the source 5, the shell ends 1024.1,1024.2 and, in systems having two mirror segments, also the transitionregion between the first mirror segment 1007.1, 1007.2 and the secondmirror segment 1009.1, 1009.2, define an optically used region or a beampipe through which the radiant flux flows from the object and/or fromthe light source 1 to the image 5 of the light source. A meridiansection or a meridional plane is the plane which includes the axis ofrotation RA. An unused region 1032 now lies between the used regions1030.1, 1030.2 of at least two mirror shells 1004.1, 1004.2 positionedone inside the other. This region is completely in the shadow region ofthe inner collector shell 1004.1. In addition, the unused region, as inthe present exemplary embodiment and in the exemplary embodiment shownin FIGS. 15 and 16, may be in a forward aperture gap 1000, i.e., a gapbetween the ring aperture elements 1002.1, 1002.2. This object-sideaperture gap 1000 is not transferred into the image 5 of the lightsource and therefore remains unused.

Further components of the nested collector may be positioned in theunused region 1032 between two mirror shells 1004.1, 1004.2 withoutinfluencing the radiant flux from the light source 1 to the image 5 ofthe light source. Examples of components of this type would be detectorsor decoupling mirrors which deflect light onto detectors or non-opticalcomponents such as heat shields or cold traps. The cooling devices1006.1, 1006.2, 1006.3 may be in direct contact with the backs of thecollector shells. The arrangement of electrodes or magnets to deflectcharged or magnetic particles is also possible. Electrical lines orlines to supply and remove coolant may be guided with only slightshadowing of the image-side collector aperture, i.e., the illuminatedregion in the image-side plane still outside the collector. These lines1044 are preferably guided in the region of the shadows of the necessarysupport devices of the mirror shells, for example, the spoked wheelhaving spokes 1010. Naturally, further cooling elements or detectors mayalso be positioned in regions outside the outermost shell 1004.2 or thecentral shadowing 1052. A diaphragm may also preferably be positioned inthe region of the central shadowing, as is shown in FIG. 8, for example.

A further exemplary embodiment of the present invention is shown in FIG.25. The exemplary embodiment shown in FIG. 25 again shows a systemhaving two mirror shells 1104.1, 1104.2. Identical components as in FIG.24 have a reference number increased by 100. In contrast to theembodiment in FIG. 24, the collector shown in FIG. 25 is a system inwhich each mirror shell includes only one single segment 1107.1, 1109.1,specifically the segment of an ellipsoid. Furthermore, the ring apertureelement has no gaps. In the present case, an annular cooling device1106.1, 1106.2, in the form of annular plates, for example, ispositioned in the unused region 1132 between the two mirror shells1104.1, 1104.2. The annular plates again preferably have a coolantflowing through them. The coolant is supplied and removed via coolantlines 1144, which lead from the cooling plate 1106.1, 1106.2 to a spoke1110, which mounts the individual mirror shells as described above. Theimplementation of the cooling device as an annular plate allows ahomogeneous and rotationally symmetric cooling to be achieved over alarge area. The plates may be connected permanently to the mirror shell,through galvanic deposition, for example. The heat is then removedthrough thermal conduction. Alternatively, the shells may also be merelylaid in place. In this way, mutual influence due to thermal expansion ofthe mirror shell and/or the cooling plate is avoided. The heat is thenremoved exclusively through radiation.

The cooling devices may also be implemented as cooling rings whichextend around the entire circumference of the collector. Cooling ringsand particularly their support are shown in FIG. 26. The cooling rings1200.1 and 1200.2 are positioned in the unused space between two mirrorshells of a collector having, for example, two segments per mirrorshell. A two-shell Wolter collector of this type is illustrated inmeridional section in FIG. 24, for example. The cooling rings 1200.1,1200.2 are supported on holding structures and/or ribs 1202.1, 1202.2,1202.3, 1202.4, which run in the shadows of the spokes of the spokedwheel and extend in the direction of the axis of rotation. The coolingrings 1200.1 and 1200.2 may be connected to the support ribs 1202.1,1202.2, 1202.3, 1202.4 via soldering, for example. This guarantees goodmechanical and thermal contact. The ribs are preferably manufacturedfrom a material having good thermal conductivity, copper, for example,and are easily solderable. The cooling rings 1202.1, 1202.2 arepreferably also made of a material having good thermal conductivity suchas copper or steel.

The ribs 1202.1, 1202.2, 1202.3, 1202.4 are attached, using screws, forexample, to the four spokes 1204.1, 1204.2, 1204.3, 1204.4 of a spokedwheel, which mounts the individual mirror shells. The spokes run in theradial direction, i.e., in a direction perpendicular to the axis ofrotation.

Using the present invention, a collector is specified for the first timewhich images any arbitrary light source in an image of the source. Thesource image may be real, virtual, or lie in the infinite. The emissioncharacteristic of the arbitrary light source is transformed in such away that a largely homogeneous illumination results in a plane in frontof or behind the intermediate image.

It should be understood by a person skilled in the art, that thedisclosure content of this application comprises all possiblecombinations of any element(s) of any claims with any element(s) of anyother claim, as well as combinations of all claims amongst each other.

1. A collector comprising: a first mirror shell positioned inside asecond mirror shell that has a chamfered end.
 2. The collector of claim1, wherein said collector receives light from a light source andreflects said light to illuminate an area in a plane.
 3. The collectorof claim 2, wherein said chamfered end receives said light from saidlight source.
 4. The collector of claim 1, wherein said second mirrorshell includes a portion that receives light and reflects said light,and wherein said chamfered end receives said light from said portion,and further reflects said light.
 5. The collector of claim 1, whereinsaid second mirror shell has a thickness that decreases in a directionof said chamfered end.
 6. The collector of claim 1, wherein said firstmirror shell receives light from a light source at an angle of incidenceof less than 20° to a surface tangent of said first mirror shell, andwherein said second mirror shell receives light from said light sourceat an angle of incidence of less than 20° to a surface tangent of saidsecond mirror shell.
 7. The collector of claim 1, wherein at least oneof said first and second mirror shells includes a first segment having afirst optical surface and second segment having a second opticalsurface.
 8. The collector of claim 7, wherein said first segment isannular in a section of a hyperboloid, and wherein said second segmentis annular in a section of an ellipsoid.
 9. The collector of claim 7,wherein said first segment is annular in a section of a hyperboloid, andwherein said second segment is annular in a section of a paraboloid. 10.An illumination system comprising: a light source; a plane; and acollector that receives light from said light source, and illuminates anarea in said plane, wherein said collector has a first mirror shellpositioned inside a second mirror shell that has a chamfered end. 11.The illumination system of claim 10, further comprising an opticalelement having a plurality of raster elements in a light path from saidlight source to said plane.
 12. The illumination system of claim 11,wherein said collector illuminates an annular region in said plane, andwherein said plurality of raster elements are in said annular region.13. An EUV-projection exposure facility comprising: the illuminationsystem of claim 10 for illuminating a mask; and a projection objectivefor imaging said mask onto a light sensitive object.
 14. A method ofmanufacturing a micro-electronic component, comprising using theEUV-projection exposure facility of claim 13.